The present invention relates generally to industrial process field devices, and more particularly to a modular terminal assembly for wireless process variable transmitters.
The term “field device” covers a broad range of process control and monitoring devices that measure and control parameters such as pressure, temperature, and flow rate. Many field devices include transceivers which act as communication relays between an industrial process variable sensor and a remote control or monitoring device such as a computer. The output signal of a sensor, for example, is generally insufficient to communicate effectively with a remote control or monitoring device. A field device bridges this gap by receiving communication from the sensor, converting this signal to a form more effective for longer distance communication (for example a modulated 4-20 mA current loop signal, or a wireless protocol signal), and transmitting the converted signal to the remote control or monitoring device.
Field devices are used to monitor and control a variety of parameters of industrial processes, including pressure, temperature, viscosity, and flow rate. Other field devices actuate valves, pumps, and other hardware of industrial processes. Each field device typically comprises a sealed enclosure containing actuators and/or sensors, electronics for receiving and processing sensor and control signals, and electronics for transmitting processed sensor signals so that each field device and industrial process parameter may be monitored remotely. Large scale industrial manufacturing facilities typically employ many field devices distributed across a wide area. These field devices usually communicate with a common control or monitoring device, allowing industrial processes to be centrally monitored and controlled.
Field devices increasingly use wireless transceivers to communicate with centralized control and monitoring systems. Wireless devices extend the reach of control or process monitoring systems beyond that of wired devices to locations where wiring may be difficult, unsafe, or expensive to provide. In some cases, wireless field devices may be powered by direct electrical connection to power utilities such as 120V AC utilities. More often, however, power utilities are not located nearby or cannot readily be installed in hazardous locations where instrumentation and transducers must operate. Accordingly, field devices are often locally powered by power sources with limited capacity, either stored, as in the case of a long-life battery, or produced, as in the case of an energy harvester. Batteries, for instance, are typically expected to last more than five years, and preferably as long as the life of the field device. Because local power sources have limited capacities, the use of lower power electronics and RF radios is frequently essential for many wireless field devices.
Many field device designs enclose an attached battery under a cover of the sealed enclosure of the field device. Other field devices utilize power from external sources (e.g. nearby utility grids or energy harvesters such as solar panels, vibrational scavengers, or thermoelectric scavengers). Each method of powering a wireless field device conventionally requires a different wiring terminal interface. Field devices which run partly or entirely on battery power typically incorporate small terminal blocks which provide connection points to an attached battery. These small terminal blocks are housed in narrow spaces between the sealed interior of the field device and the attachment point of the battery. Wireless field devices which run on grid power, by contrast, include terminal blocks which provide wired connections for grid power (typically via screw terminals), and which condition grid power for use by the field device. Solar panels, vibrational energy scavenging systems, and other types of local power modules may all use different terminal blocks. In addition, different field device models may require different terminal block parts which are not necessarily intercompatible. A first field device model might, for instance, require a first terminal block part to receive battery power, a second to receive grid power, and a third to receive solar power. A second field device model might utilize fourth, fifth, and sixth terminal block parts to make the same battery, grid, and solar power connections. Complex industrial processes monitored or actuated via a large number of diverse models of field devices running on a variety of power sources can utilize many different kinds of terminal blocks, making it impractical or inconvenient to store replacements for each.